Field of the Invention
The invention lies in the automotive field. More specifically, the invention relates to a brake pedal configuration, in particular to such a configuration for an automobile equipped with electrically actuated wheel brakes. The system detects actuations of a brake pedal by means of sensors and it is provided with a spring configuration that opposes the brake actuation forces exerted on the brake pedal with a resistance force and that has a nonlinear spring characteristic.
In conventional automobile brake systems, the braking force is generated by the driver via the brake pedal. The force is usually boosted and transmitted via hydraulic delivery lines to the wheel brake cylinders. In power brake systems, there is no mechanical, pneumatic or hydraulic connection between the actuating unit, that is to say the brake pedal, and the wheel brakes. Although the driver, by actuating the brake pedal, can influence the braking force by means of suitable control devices, his physical strength is not utilized either fully or partially for generating the braking force when the brake pedal is actuated. If the power brake system is controlled electronically and the wheel brakes are actuated by means of electric energy, then it is necessary, in order to detect the driver's deceleration request, to have a special brake pedal configuration which detects actuations of the brake pedal by means of sensors and generates electric signals which are transmitted in electronic form to a brake control unit (see German patent DE 196 15 186 C1; and ATZ 98, 1996, No. 6, pages 328-32).
In conventional hydraulic brake systems, the pedal characteristic can be modified only within very narrow limits. This is so because, due to the hydraulic coupling between the actuating unit and the wheel brakes, this characteristic depends on the design of the brake system, that is to say the size of the wheel brake cylinders and the design of the brake booster and hydraulic fluid volume.
The force/travel characteristic of a known brake pedal for activating an electric brake system is generated by means of a cup spring assembly which is connected to the brake pedal via a rod that is articulated at the pedal (German published patent application DE 195 40 705 A1). There, the cup spring assembly is composed of cup springs having different characteristics.
In another published brake pedal configuration for electric brake systems (European EP 0 708 006 A1), the reactive force to the actuation of the brake pedal is generated by two helical springs which have different spring characteristics and which surround a piston rod that is articulated at the brake pedal.